Electronic fan regulator

Was just curious to know how these work and came across different versions. Some using DIAC /TRIAC combos and some like the one shown here ... basically uses capacitor as voltage droppers instead of the power wasting resistive droppers.

How effective is this circuit and does it also lead to " hum" when controlling ?

Very. Its main weaknesses are that the load needs to be constant because you set the voltage drop by exploiting the reactance of the capacitor, and this is fixed with the choice of a capacitor value. And also the capacitors can get large depending on the application. It works really well and it's often used to power small DC-powered devices run directly from a wall socket with a relatively stable current draw, although in these applications, I increasingly see miniature switch-mode power supplies being used. However, for an AC fan, the capacitor circuit is still cheap and easy to construct, and it's very reliable.

I think the hum is more an issue of resonant frequency and therefore unrelated to how the device is powered.

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